Quantitative Analysis of the Rate of Geochemical Weathering of Sulfur from Sedimentary Rocks Using Atmospheric Deposition, Concentration and River Discharge Data

Abstract

Quantitative analysis of the rate of geochemical weathering of sulfur (<i>S</i>) from sedimentary rocks (<i>GeoS</i>) was conducted using concentration (<i>Cs</i>) and discharge (<i>Qs</i>) data from the Tedori River and atmospheric deposition (<i>AtdepS</i>) in the basin. First, <i>S</i> fluxes were calculated using 16 years of <i>Cs</i> and <i>Qs</i> data. The annual average discharge of <i>S</i> (<i>TotalS</i>) was estimated at 8597<span> </span>ton·year<i>^-</i>¹ (117.3 kg·ha<i>^-</i>¹·year<i>^-</i>¹). Of this, 1331 ton·year<i>^-</i>¹ was <i>AtdepS </i><span>(</span>18.2 kg·ha<i>^-</i>¹·year<i>^-</i>¹) and another 7266 ton·year<i>^-</i>¹ was <i>GeoS</i> (99.1 kg·ha<i>^-</i>¹·year<i>^-</i>¹). Monthly changes in <i>TotalS</i> were investigated, which showed that <i>GeoS</i> was highest in summer, because of the air temperature, while <i>AtdepS</i> peaked in winter because of seasonal wind. Using <i>Qs</i> and <i>AtdepS</i> corrected for altitude, <i>TotalS</i>, <i>AtdepS</i> and <i>GeoS</i> were estimated at six sites, and among these sites we found that the <i>TotalS</i> per unit area values were random, depending on the site characteristics. In particular, the discharge from the Kuwajima site was remarkably high suggesting that the sedimentary rocks at this site had higher pyrite content than at the other sites. Finally, we also assessed the relationship between the characteristics of sedimentary rocks and <i>GeoS</i> in a range of rivers in the Hokuriku Region, and found that there was a close relationship between concentrations of <span>SO₄^2-</span> greater than 10 mg·l<i>^-</i>¹ and sedimentary rocks containing the pyrite group. In addition, we estimated that the influence of <i>GeoS</i> was present when the concentration of<span> SO₄^2-</span> in river water was greater than 2<span> - </span>3 mg·l<i>^-</i>¹ in the Hokuriku region.<span></span> <p> </p